Radial piston fluid working machines, such as radial piston pumps, motors or pump/motors, typically comprise a central crankshaft which is rotatable about an axis of rotation and a plurality of piston cylinder devices arranged about and extending radially outwards from the crankshaft. The piston cylinder devices are typically arranged in a plurality of axially offset banks of piston cylinder devices, each bank comprising a plurality of closely packed piston cylinder devices arranged about the axis of rotation and lying on a respective plane extending perpendicularly to the axis of rotation of the crankshaft. The crankshaft comprises at least one cam per bank, and the pistons of each respective bank are arranged in driving relationship with the respective said at least one cam via respective piston feet.
The magnitude of the output (e.g. fluid pressure or mechanical torque) of such radial piston fluid working machines is typically dependent on the number of piston cylinder devices provided in the machine and the capacity of each of the said piston cylinder devices. An increased output magnitude therefore requires an increase in the number of banks and/or an increase in the number of piston cylinder devices per bank and/or an increase in the capacity of the piston cylinder devices used. Increasing the number of banks per machine causes a corresponding increase in the axial length of the machine. The extent to which the number of piston cylinder devices per bank can be increased is dependent on the relative sizes of the piston feet and the cam radius. As the piston cylinder devices are typically closely packed around the axis of rotation of the crankshaft, increasing the number of piston cylinder devices typically requires an increase in the radius of the cams, which correspondingly increases the size of the fluid working machine in a radial direction. Accordingly, an increased output magnitude typically requires an increase in the size of the fluid working machine in radial and/or axial directions.
Fluid working machines of this type are used in hydraulic transmission systems for high power wind turbines. As wind turbine technology develops, higher power turbines are being implemented whose hydraulic transmissions require greater output magnitudes. However, it is desirable to keep the size of the wind turbines as small as possible.
In addition, in order to route fluid from fluid sources, to fluid sinks and to and from working chambers of the piston cylinder devices, complex fluid routing structures can be required, leading to expensive and time consuming manufacturing processes. It is thus also desirable to simplify the way in which fluid is routed around the fluid working machine.